1. Field of the Invention
The invention relates generally to Serial Attached SCSI (SAS) domains and more specifically relates to enhanced SAS expanders.
2. Discussion of Related Art
In SAS domains (i.e., electronic systems implementing a switched SAS fabric) it is common for a controller to manage a large number of logical volumes of data. The logical volumes are provisioned by SAS/SATA storage devices, which may be coupled for communication with the controller via one or more SAS expanders. The SAS expanders establish switched temporary communication channels between the controller and the various storage devices.
Common tasks performed by a controller when managing logical volumes include processing input and output (I/O) commands from a host device, performing consistency checks on the logical volumes, backing up the volumes, etc. However, backing up a logical volume takes up substantial amounts of processing power at the controller, because the controller generates and transmits a vast number of I/O commands to various storage devices as it backs up data to the volume. This is undesirable because the backup occupies processing resources at the controller that could otherwise be used to process host I/O. Furthermore, the backup process can reduce the available bandwidth of the entire SAS domain, because communication channels between the controller and the expanders that route backup I/O to the appropriate storage devices may be occupied for the entire duration of the backup process. This precludes other connections that would use the same pathways through the SAS expanders.
Thus it is an ongoing challenge to enhance the performance of a controller in processing host I/O when a logical volume is backed up.